The spinal clamping systems of the prior art are generally composed of two hooked devices for fixing a disabled vertebra and of fasteners such as nuts and bolts for fastening the two hooked devices holding the disabled vertebra. The case in point is the interlaminar clamp system bearing the trademark of HALIFAX and made by the AME Corporation of the United States. Such spinal clamping systems of the prior art are defective in design in that the fastening effect of the hooked devices is often seriously undermined by the fact that the spinal movement can cause the nuts and the bolts to become loosened. Such defective design of the prior art spinal clamping systems is discussed by Ronald Moskovich, et al. in an article entitled "Altantoaxial Arthrodesis using Interlaminar Clamps", which was published in SPINE, 17 (3), 261 (1992). For details, please refer to FIG. 5 and the accompanying text therefore in the article.
In addition, the spinal clamping systems of the prior art are further limited in that they can not be used to bring about an auxiliary fixation between two vertebral locking rods.
With a view to overcoming the shortcomings of the spinal clamping systems of the prior art, this inventor of the present invention developed several improved spinal clamping systems, which were disclosed respectively in the U.S. patent application Ser. Nos. 08/004,612 (filing date: Jan. 14, 1993), 08/004,609 (filing date: Jan. 14, 1993) and 08/004,610 (filing date: Jan. 14, 1993). The improved spinal clamping system, which was disclosed in the U.S. patent application Ser. Nos. '612 and '610, is of a dual-layer system and composed of screws and slotted plates for use in adjusting the distance between the two hooked portions. The improved spinal clamping system disclosed in the U.S. patent application Ser. No. '609 is of a reversible clamping system and composed of reversible clamping members having a plurality of bevel clamping slots for use in adjusting the distance between two hooked portions. These improved spinal clamping systems described above are limited in design in that the distance between the two hooked portions can not be adjusted at will, and that the dual-layer locking effect of the vertebra is often compromised by the excessively protruded portions of the systems.